Ceramic particle filled and ceramic particle coated battery separators for secondary lithium batteries are known, for example as described in respective U.S. Pat. No. 7,790,320 and U.S. Pat. No. 6,432,586, each hereby incorporated herein by reference. It is believed that these separators improve the safety of the secondary lithium battery by, for example, blocking dendrites, preventing shorting, enhancing the heat resistance and rigidity (strength and structure) of the polymeric (e.g., polyolefin) layer. Typically, the prior art particles consisted of rather large (some with particle size>1 micron) SiO2, TiO2, Al2O3, BaSO4, CaCO3, and the like particles. These ceramic particles, however, may be difficult to load and disperse into the polymeric material because of the difference in surface energy between the particles and the polymeric resin material. These problems become even greater as the particle size is moved from the micron range to the nanometer range because the surface energy of the particles increases even more.
Therefore, the problem is to load and disperse at least certain ceramic particles into a polymeric resin used to form a membrane, e.g., a battery separator.